Method for instilling a predetermined volume of medicament into an eye

ABSTRACT

An apparatus is used to apply medicament to an eye and stores the medicament in a medicament chamber. A nozzle is coupled in fluid communication with the medicament chamber and is formed by an outer nozzle portion and an inner nozzle portion received within the outer nozzle portion. A seam is formed by the interface of the inner nozzle portion and the outer nozzle portion and is normally in a closed position to prevent the passage of medicament through the nozzle. The seam opens in response to the flow of medicament of sufficient pressure into the seam to permit the passage of medicament through the nozzle for release into the eye.

This application is a divisional application of Ser. No. 08/433,856filed on May 2, 1995, now U.S. Pat. No. 5,685,869, which was a divisionof application Ser. No. 08/209,957 filed on Mar. 11, 1994, now U.S. Pat.No. 5,613,957, which was in turn a continuation of Ser. No. 07/801,243originally filed on Dec. 2, 1991, now abandoned.

FIELD OF THE INVENTION

The present invention relates to apparatus for dispensing fluid througha nozzle, such as ocular treatment apparatus for applying medicament orother substances to an eye.

BACKGROUND INFORMATION

There are various known devices for applying medicament to the eye. Atypical eye-drop container has a flexible vial and a nozzle forreleasing drops of medicament into the eye by squeezing the vial. If theuser squeezes too hard, too much medicament can be released and, as aresult, drip down the user's cheek. There is typically no means providedfor accurately controlling the volume of each dose of medicamentreleased into the eye. Also, if the tip of the nozzle becomescontaminated, there is typically no means provided for preventing thecontaminated tip from contaminating the medicament within the vial, andthus possibly causing infection by use of the contaminated medicament.Because the medicament in such devices is typically exposed to air uponopening the nozzle, it is not desirable to use such devices toadminister preservative-free formulations of medicament, other than byproviding single-dose containers. The single-dose containers, however,are typically relatively expensive to package, particularly when usedfor prescription medications.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus for applyingmedicament to an eye, comprising a medicament chamber for holdingmedicament, and a nozzle coupled in fluid communication with themedicament chamber. The nozzle defines a seam which is normally in aclosed position for preventing the passage of medicament through thenozzle and which opens in response to the flow of medicament ofsufficient pressure to permit the passage of the medicament through thenozzle for release into the eye.

In one apparatus of the present invention, the nozzle includes an outernozzle portion and an inner nozzle portion received within the outernozzle portion, and the seam is defined by the interface of the innerand outer nozzle portions. The outer nozzle portion is preferably madeof a more flexible material in comparison to the inner nozzle portionfor facilitating the opening of the seam in response to the flow ofmedicament of sufficient pressure for release through the nozzle intothe eye.

In one embodiment of the present invention, the apparatus furthercomprises a piston member for pressurizing medicament to flow throughthe seam of the nozzle for release into the eye. The piston member isseated within a piston cavity coupled in fluid communication with thenozzle and the medicament chamber, and the piston member is moveablewithin the piston cavity to push medicament within the piston cavitythrough the seam for release into the eye. The piston cavity ispreferably dimensioned to release a predetermined volume of medicamentinto the eye.

In another embodiment of the present invention, the apparatus comprisesan actuating member for pressurizing medicament to flow into the seamfor release into the eye. The actuating member is preferably coupled toa shaft member and moveable along the shaft member to pressurizemedicament to flow into the seam. The shaft member defines at least onechannel coupled in fluid communication with the seam for directing theflow of pressurized medicament upon movement of the actuating memberalong the shaft member into the seam. An apparatus of the presentinvention further comprises a flange member coupled to the shaft memberfor directing the flow of medicament pressurized upon movement of theactuating member toward the seam.

An apparatus of the present invention further comprises a wall defininga cavity coupled in fluid communication with the medicament chamber forreceiving the flange member upon movement of the actuating member alongthe shaft member toward the flange member. The medicament within thecavity is pressurized by movement of the actuating member and directedinto the seam. The wall defines at least one aperture for coupling thecavity in fluid communication with the medicament chamber, and themedicament within the cavity is directed into the seam upon movement ofthe actuating member toward the flange member.

One advantage of the apparatus of the present invention is that once adose of medicament is released, the seam of the nozzle closes, and thussubstantially prevents medicament which may have been exposed to air orforeign particles from passing back through the nozzle and into theapparatus, which can contaminate the remainder of medicament in theapparatus. Thus, the apparatus of the present invention is particularlysuitable for storing multiple-dose quantities of medicament, because itsubstantially prevents the remainder of the medicament from becomingcontaminated once the apparatus is used. The apparatus of the presentinvention is also particularly suitable for use with preservative-freeformulations of medicament or other substances which require that eachtime a dose of fluid is released, that the remainder of the fluid remainin a contaminant-free environment. The apparatus of the presentinvention is also particularly suitable for use with medicaments whichshould not be exposed to air because of an undesirable chemicalreaction, for example, prior to use.

Another advantage of the apparatus of the present invention is that asubstantially predetermined volume of medicament can be released intothe eye each time the apparatus is actuated. Accordingly, the apparatusof the present invention should substantially facilitate patientcompliance with treatment. Other advantages of the apparatus of thepresent invention will become apparent in view of the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an apparatus embodying the presentinvention.

FIG. 2 is a cross-sectional view of the nozzle of the apparatus of FIG.1 taken along the line 2--2 of FIG. 1.

FIG. 3 is a cross-sectional view of another apparatus embodying thepresent invention.

FIG. 4 is a cross-sectional view of the apparatus of FIG. 3 illustratedin an actuated position for releasing a dose of medicament through thenozzle.

DETAILED DESCRIPTION

In FIG. 1, an apparatus embodying the present invention is indicatedgenerally by the reference numeral 10. The apparatus 10 includes anouter body 12, an inner body 14 fitted within the outer body 12, and apiston body 16 coupled to the outer body 12. The piston body 16 includesa piston 18 projecting into the inner body 12 substantially in the axialdirection of the apparatus. The outer body 12 and inner body 14 define anozzle 20 for releasing drops of medicament into a user's eye uponmovement of the piston body 16, and thus the piston 18 relative to theouter body 12, as is described further below.

The outer body 12 defines an outer nozzle portion 22 which receives aninner nozzle portion 24 of the inner body 14. As shown in FIGS. 1 and 2,a seam 25 is formed by the interface of the outer nozzle portion 22 andthe inner nozzle portion 24 which is formed by the abutting surfaces ofthese two portions which taper inwardly toward the tip of the nozzle 20.The seam 25 is normally closed, but is opened when medicament ofsufficient pressure is forced into the seam to release the medicamentthrough the nozzle 20. The outer body 12 is preferably molded from arelatively flexible plastic material in comparison to the inner body 14.Thus, the outer nozzle portion 22 can be flexed relative to the innernozzle portion 24 to permit the passage of medicament through the seam25 and out of the nozzle 20, as is described further below. In theembodiment of the present invention illustrated, the outer body 12 ispreferably made of a thermoelastic plastic, such as the plastic soldunder the name "Kraton" by the Shell Company. The inner body 14 ispreferably made of a more rigid plastic, such as the plastic sold underthe name "Valox", by the General Electric Company. These particularplastic materials are only exemplary, however, and other types ofplastics can be used that are within the knowledge of those skilled inthe art.

The outer body 12 includes an annular flange 26 which fits within acorresponding recess in the inner body 14, as shown in FIG. 1. The innerbody 14, on the other hand, includes an annular lobe 28 which fitswithin a corresponding recess in the outer body 12. The inner body 14 istherefore pressed into the outer body 12 and coupled to the outer bodyby guiding the flange 26 and snapping the lobe 28 into the correspondingrecesses.

The outer body 12 further includes a bellows 30 and a flange 32, whichis in turn coupled to the piston body 16. A medicament chamber 33 isthus defined within the outer body 12 and the piston body 16, as shownin FIG. 1. The piston body 16 includes a lobe 34 which is snapped into acorresponding recess in the flange 32 to couple the piston body to theouter body 12, as shown in FIG. 1. The bellows 30 is adapted to flexinwardly to permit the piston body 16 and piston 18 to move relative tothe outer and inner bodies 12 and 14, respectively, as indicated by thearrows in FIG. 1, to release medicament from the medicament chamber 33through the nozzle 20.

The inner body 14 includes a substantially cylindrical wall 36 whichprojects toward the piston body 16 and slidably receives the piston 18,as shown in FIG. 1. The cylindrical wall 36 defines a drop cavity 38located below the piston 18, which is adapted to hold a predeterminedvolume of medicament for release through the nozzle 20 into the eye. Thedrop cavity 38 is preferably dimensioned to hold less than 30microliters of medicament, and for many medicaments, a quantitypreferably within the range of 15 to 20 microliters. However, thiscapacity is purely exemplary, and can be changed as desired.

As shown in FIG. 1, the piston 16 includes a flexible rim 40 on its freeend which is adapted to be maintained in sliding contact with thecylindrical wall 36. The inner body 14 further includes a knob 42projecting from an interior surface toward the piston 18, and a channel44 extending between the seam 25 and the drop cavity 38. The cylindricalwall 36 includes a pair of slots 46, each extending from the top of thedrop cavity 38 to the free end of the cylindrical wall.

When the piston 18 is in the up position, i.e., the tip of the rim 40 islocated above the base of each slot 46, medicament is permitted to flowfrom the medicament chamber 33 through the slots 46 and into the dropcavity 38. In FIG. 1, the piston 18 is shown in approximately the middleof its stroke. Then, on the downward stroke of the piston 18 (i.e.,toward the nozzle 20), the medicament in the drop cavity 38 is forcedthrough the channel 44 and into the seam 25. The pressurized medicamentopens the seam 25 by causing the outer nozzle portion 22 to flexrelative to the inner nozzle portion 24 to release the medicament intothe eye. Then, once the medicament in the drop cavity 38 is released,the seam 25 returns to its normally closed state (i.e., the inner nozzleportion 24 is maintained in contact with the outer nozzle portion 22) toprevent air or foreign particles from passing through the nozzle andcontaminating the remaining medicament within the apparatus.

The apparatus 10 further includes a medicament container 48 coupled onone end to the piston body 16 for holding medicament. The container 48is preferably made of a plastic material and is sealed to the pistonbody 16 by welding, for example. The other end of the container 48 (notshown) is also sealed in a manner known to those skilled in the art. Thepiston body 16 includes several apertures 50 extending through its topwall to couple the container 48 in fluid communication with themedicament chamber 33. Medicament is therefore permitted to flow fromthe container 48, into the medicament chamber 33, and into the dropcavity 38 for release into the eye.

The apparatus 10 is preferably mounted within an ocular treatmentapparatus substantially the same as the apparatus shown and described inU.S. Pat. No. 4,981,479, dated Jan. 1, 1991, which is assigned to thesame assignee as the present invention, and is hereby expresslyincorporated by reference as part of the present disclosure. Theapparatus 10 is mounted within an ocular treatment apparatus as shown inU.S. Pat. No. 4,981,479 in place of the ocular vial shown in thatpatent. Additional modifications that are necessary in order to use theapparatus 10 with such an ocular treatment apparatus will be known tothose skilled in the pertinent art, particularly in view of theteachings of U.S. Pat. No. 4,981,479. The outer body 12 is seatedagainst a surface of the ocular treatment apparatus, as indicated inphantom lines in FIG. 1, in order to be maintained in a stationaryposition. A coil spring 52 is preferably seated between a surface of theocular treatment apparatus and an annular flange 54 on the piston body16, as also shown in FIG. 1. The coil spring 52 is provided to drive thepiston body 16 to return to its normal position upon releasingmedicament, as is described further below.

In the operation of the apparatus of the present invention, when thepiston body 16 is located in the up position, medicament is permitted toflow from the medicament chamber 33, through the slots 46, and into thedrop cavity 38 to fill the drop cavity. Then, when the piston body 16 ispushed toward the outer body 12 and into the down position, the downwardstroke of the piston 18 forces the medicament in the drop cavity 38through the channel 44 and into the seam 25.

On the downward stroke of the piston 18, the flexible rim 40 is forcedoutwardly into contact with the cylindrical wall 36, thus preventing thepassage of medicament in the drop cavity 38 back into the medicamentchamber 33. The pressurized medicament flowing through the channel 44opens the seam 25 by forcing the flexible outer nozzle portion 22 awayfrom the inner nozzle portion 24 to open the nozzle and release themedicament. Then, once the medicament is released, the outer nozzleportion 22 returns to its normal position in contact with the innernozzle portion 24 so as to close the seam 25, and thus prevents thepassage of medicament (which may be exposed to air or foreign particles)through the nozzle 20 and back into the drop cavity 38, which mightotherwise contaminate the remaining medicament in the apparatus. Thecoil spring 52 then drives the piston body 16 and piston 18 back towardthe up position causing a suction to develop within the drop cavity 38.Then, when the piston 18 reaches the up position, the suctionfacilitates the flow of medicament in the medicament chamber 33 into thedrop cavity 38 and the apparatus 10 is ready to release another dose ofmedicament.

As will be recognized by those skilled in the art, one advantage of theapparatus of the present invention is that the nozzle 20 prevents thepassage of medicament which has been exposed to air or foreign particlesfrom entering the apparatus, and thus substantially preventscontamination of the medicament remaining within the apparatus. Anotheradvantage of the apparatus 10 is that the pumping mechanism, whichincludes the piston 18, the cylindrical wall 36, and the drop cavity 38,is entirely enclosed within the contaminant-free environment of themedicament chamber 33. These advantages are particularly beneficial whenusing the apparatus to dispense preservative-free formulations ofmedicaments or other substances which cannot be exposed to air orforeign matter prior to use.

In FIGS. 3 and 4 another apparatus embodying the present invention isindicated generally by the reference numeral 110. The apparatus 110 issimilar to the apparatus 10 described above, and therefore likereference numerals preceded by the numeral 1 are used to indicate likeelements. The apparatus 110 includes an outer body 112, an inner body114 fitted within the outer body 112, and a piston body 116 coupled tothe outer body 112. The outer body 112 and inner body 114 define anozzle 120 for releasing drops into a user's eye upon movement of thepiston body 116 relative to the outer body 112, as indicated by thearrows in FIGS. 3 and 4. The nozzle 120 is the same as the nozzle 20.

The outer body 112 defines an outer nozzle portion 122 which receives aninner nozzle portion 124 of the inner body 114. The interface of theouter nozzle portion 122 and the inner nozzle portion 124 defines a seam125 which is normally closed (i.e., the inner and outer nozzle portionsare abutting one another as shown in the drawings), but can be opened bythe flow of medicament of sufficient pressure into the seam to releasethe medicament through the nozzle 120. As with the nozzle 20 describedabove, the outer body 112 is preferably molded from a relativelyflexible plastic material in comparison to the inner body 114. Thus, theouter nozzle portion 122 can be flexed relative to the inner nozzleportion 124 to open the seam 125 to release the medicament through thenozzle 120.

The outer body 112 includes an annular flange 126 which fits within acorresponding recess in the inner body 114, as shown in FIGS. 3 and 4.The inner body 114, on the other hand, includes an annular lip 128 whichretains the inner body 114 within the outer body 112. The inner body 114is therefore pressed into the outer body 112 and coupled to the outerbody by guiding the flange 126 into the corresponding recess andsnapping the outer body 114 within the lip 128 of the inner body.

The outer body 112 further includes a bellows 130 and a flange 132coupled to the piston body 116. A medicament chamber 133 is thus definedwithin the outer body 112 and within the piston body 116, as shown inFIGS. 3 and 4. The piston body 116 includes an aperture 135 to permitthe medicament within the chamber 133 to flow between the interior ofthe outer body 112 and the interior of the piston body 116. The pistonbody 116 includes a lobe 134 which is snapped into a correspondingrecess in the flange 132 to couple the piston body to the outer body112, as shown in FIGS. 3 and 4. As will be recognized by those skilledin the art, however, the outer body 112 and piston body 116 can equallybe molded as an integral body to further prevent any leaks within theapparatus due to changes in the ambient pressure or temperature, forexample.

The outer end of the piston body 116 is sealed in a manner known tothose skilled in the art to retain the medicament within the medicamentchamber 133. The other end of the piston body 116 can also be coupled toanother container, for example, for pre-packaging the medicament in amanner known to those skilled in the art. The bellows 130 is adapted toflex inwardly to permit the piston body 116 to move relative to theouter body 112 to release medicament stored within the medicamentchamber 133 through the nozzle 120.

The inner body 114 includes a first substantially cylindrical wall 136essentially defining a hollow shaft projecting in the axial direction ofthe apparatus 110 and surrounding a rod member 118, as shown in FIGS. 3and 4. A first channel 138 is defined between the rod member 118 and thefirst cylindrical wall 136, and a second channel 140 extends between thefirst channel 138 and the seam 125.

The piston body 116 includes a bushing 142 which receives the firstcylindrical wall 136, and thus guides the piston body 116 as it is movedalong the first cylindrical wall. As shown in FIGS. 3 and 4, theinterior surface of the bushing 142 defines a generally concave profilefor engaging the cylindrical wall 136 in a fluid-tight manner, and thussubstantially prevents the flow of medicament between the bushing 142and the cylindrical wall 136 upon moving the piston body 116 to releasemedicament.

The piston body 116 further includes a second cylindrical wall 144 whichis substantially concentric with the first cylindrical wall 136, anddefines at least two slots 146 coupling the interior of the secondcylindrical wall 144 in fluid communication with the medicament chamber133. As shown in FIGS. 3 and 4, the rod member 118 is coupled to thefirst cylindrical wall 136 by means of a lobe 148 which snaps into acorresponding recess in the first cylindrical wall. A flange 150 on theend of the rod member 118 rests against the top surfaces of the firstcylindrical wall 136 and the second cylindrical wall 144 to prevent thepiston body 116 from being moved any further away from the nozzle 120.

As shown in FIGS. 3 and 4, a flange member 152 is coupled to the end ofthe first cylindrical wall 136 and tapers outwardly so that its free endengages the interior surface of the second cylindrical wall 144. Thesecond cylindrical wall 144 and the flange member 152 thus define a dropcavity 154 for holding medicament for release into the eye. The dropcavity 154 is preferably dimensioned to cause less than about 30microliters of medicament to be released each time the apparatus 110 isactuated. For many medicaments, the drop cavity 154 is preferablydimensioned to release approximately 15 to 20 microliters of medicamenteach time the apparatus is actuated. This volume of medicament is onlyexemplary, however, and can be changed as desired by changing the volumeof the drop cavity 154, for example. The free end of the flange member152 is dimensioned so that it engages the interior surface of the secondcylindrical wall 144 in order to substantially prevent the flow ofmedicament between the second cylindrical wall 144 and the flange member152 upon movement of the piston body 116, as indicated by the arrows inFIGS. 3 and 4. The first cylindrical wall 136 defines an aperture 156extending between the first channel 138 and the drop cavity 154 topermit the flow of medicament from the drop cavity 154, through thefirst channel 138 and second channel 140, for release through the nozzle120 into the eye.

The apparatus 110 is preferably employed for use in a device such as theocular treatment apparatus shown and described in U.S. Pat. No.4,981,479. The modifications that are necessary in order to use theapparatus 110 with such an ocular treatment apparatus will be known tothose skilled in the pertinent art, particularly in view of theteachings of U.S. Pat. No. 4,981,479. The outer body 112 is seatedagainst a surface of the ocular treatment apparatus, as indicated byphantom lines in FIGS. 3 and 4, in order to maintain the outer body 112in a stationary position. A coil spring 158 is preferably seated betweenthe surface of the ocular treatment apparatus and an annular lip 160 onthe flange 132. The coil spring 158 is provided to drive the piston body116 to return to its normal position for dispensing medicament.

In the operation of the apparatus 110, the apparatus is normallyoriented in the position shown in FIG. 3 (i.e., the bellows 130 is in arelaxed state). The apparatus 110 is actuated to release medicamentthrough the nozzle 120 by depressing the piston body 116 toward theouter body 112, as shown in FIG. 4. As a result, the bellows 130 isdepressed inwardly and the bushing 142 is moved down toward the nozzle120, causing a suction to develop within the drop cavity 154, the firstchannel 138 and the second channel 140. The suction facilitates the flowof medicament from the medicament chamber 133 through the slots 146 tofill the drop cavity 154 and the first and second channels 138 and 140.Once the piston body 116 reaches the end of its downward stroke, asshown in FIG. 4, the piston body is released, thus permitting the coilspring 158 to drive the piston body 116 in the opposite direction awayfrom the nozzle 120.

As a result, the bushing 142 slides back along the first cylindricalwall 136 toward the flange member 152. Then, at about the point that thebottom of each slot 146 passes over the end of the flange portion 152,the medicament in the drop cavity 154 is forced by the bushing 142through the aperture 156 and into the first channel 138. The pressurizedmedicament flows through the second channel 140, into the seam 125, andout through the tip of the nozzle 120 for release into the eye. Thepressure caused by the force of the coil spring 158 driving the bushing142 is sufficient to cause the medicament to open the seam 125 so thatthe complete dose of medicament is released into the eye. Then, once themedicament is released, the seam 125 returns to its normally closedposition to substantially prevent any medicament that is exposed to airfrom flowing back into the apparatus. The apparatus 110 is then ready tobe actuated again to release another dose of medicament.

As will be recognized by those skilled in the art, one advantage of theapparatus of the present invention is that a substantially predeterminedvolume of medicament can be released into an eye each time the apparatusis actuated. The predetermined volume released can be controlled bycontrolling the volume of the drop cavity, for example. Anotheradvantage of the apparatus of the present invention is that once a doseof medicament is released, the seam of the nozzle closes, and thussubstantially prevents medicament which has been exposed to air orforeign particles from passing through the nozzle and into theapparatus, which can, in some instances, contaminate the remainder ofthe medicament in the apparatus. This advantage is particularlyimportant when storing multiple-dose quantities of preservative-freeformulations of medicament or other substances within the apparatus.

Another advantage of the apparatus 110 is that the pumping mechanism,which includes the first cylindrical wall 136 and the actuating member142, is contained entirely within the medicament chamber 133, and thusfurther prevents any contamination of the remaining medicament withinthe apparatus when actuating the pumping mechanism. Another advantage ofthe apparatus 110 is that the medicament is dispensed upon the releaseof the piston body 116. In this way, the same quantity of medicament isreleased each time the apparatus is actuated, because it is the force ofthe coil spring 158 which causes the medicament to be dispensed from theapparatus. Thus, the apparatus 110 can be used to reliably dispensemedicament, regardless of whether a user's hand shakes, or if there arevariations in the speed of the downward stroke of the piston body 116.

I claim:
 1. A method for instilling a predetermined volume of a liquidinto an eye from a vial having a drop chamber and a nozzle, the dropchamber being in fluid communication with the nozzle, the nozzleincluding an outer nozzle portion and an inner nozzle portion receivedwithin the outer nozzle portion to define an interface at a region ofcontact between the inner and outer nozzle portions, the region ofcontact normally preventing passage of said liquid through the nozzle,wherein a flow of said liquid of sufficient pressure may be forcedthrough the interface of the nozzle to at least partially sever saidregion of contact, and wherein the outer nozzle portion is more flexiblethan the inner nozzle portion and the outer nozzle portion has athickness which continuously decreases from a first point in a directiontoward a tip of the nozzle, said method comprising the steps of:fillingthe drop chamber with a liquid to be applied to an eye, the chamberhaving a predetermined volume; and reducing the volume of said dropchamber from said predetermined volume by a predetermined extent topressurize the liquid content contained in the drop chamber and topropel a predetermined volume of said liquid contained in the chamberthrough the interface of the nozzle to at least partially sever saidregion of contact and release said liquid into an eye.
 2. The methodaccording to claim 1 wherein the liquid is a medicament.
 3. The methodaccording to claim 1 wherein the predetermined volume of the chamber,prior to the step of reducing the volume, is less than 30 microliters.4. The method according to claim 3 wherein the predetermined volume ofthe chamber, prior to the step of reducing the volume, is from 15 to 20microliters.
 5. The method according to claim 1 wherein the step ofreducing the volume of the chamber and pressurizing the liquid containedtherein is accomplished using a piston.
 6. The method according to claim1 wherein in the step of reducing the volume of the chamber, the volumeof the chamber is reduced to zero to propel all of the liquid in thechamber into the eye.
 7. A method for instilling a first predeterminedvolume of a liquid into an eye from a vial, said vial being connected toa liquid reservoir and having a drop chamber and a nozzle, the dropchamber being in fluid communication with the nozzle, the drop chamberbeing defined by a first drop-chamber-forming member and a seconddrop-chamber-forming member, the second member being movable between: afirst position, in which the first member and the second member togetherdefine said drop chamber which is in fluid communication with saidreservoir; a second position, in which the first member and the secondmember together define said drop chamber having a second predeterminedvolume and in which the drop chamber is not in fluid communication withthe reservoir; and a third position, in which the drop chamber has athird predetermined volume which is less than the second predeterminedvolume of the drop chamber in the second position, and in which the dropchamber is not in fluid communication with the reservoir; the vialfurther having a biasing element for biasing the seconddrop-chamber-forming member to the third position, said methodcomprising the steps of:filling the drop chamber with a liquid to beapplied to an eye by moving the second drop-chamber-forming member fromthe third position to the first position; and biasing the seconddrop-chamber-forming member back to the third position from one of thefirst position and the second position under the action of the biasingelement, whereby said first predetermined volume of liquid in the dropchamber corresponding to the difference between the second and thirdpredetermined volumes is propelled through the nozzle into an eye.